The present invention is for analysis of volatile compound content in an aqueous phase wherein the aqueous phase is exposed to a volume of gas and the volatile compound is permitted to enter the gas and to come to an equilibrium concentration within the gas. The gas may then be analyzed to measure gas concentration of volatile compound(s) and the gas concentration related to obtain an aqueous phase concentration. More specifically, the present invention is a method and apparatus for decreasing the amount of time needed to reach equilibrium between the gas and the aqueous phase. As used herein, the term xe2x80x9cspargexe2x80x9d includes gas sparge wherein a gas is passed through a liquid and liquid sparge wherein a liquid is passed through a gas.
Analysis of a volatile compound in an aqueous solution is well known, generally involving obtaining a sample of the volatile compound laden aqueous solution and placing it in a container with a head space filled with a gas. The volatile compound migrates from the aqueous solution into the gas until an equilibrium concentration is reached between the gas and the aqueous solution. The concentration of volatile compound is then measured in the gas phase and Henry""s law is used to obtain the concentration of the volatile compound in the aqueous solution.
Complications arising from solution handling and limited volume of aqueous solution in a sample may be overcome by placing an enclosure or cup in-situ as described in U.S. pat. No. 5,425,268 to Li et al., and shown in FIG. 1. The cup 100 has sides 102 and a top 104 with the bottom 106 open. The cup 100 is submerged into the aqueous solution 108 with the open bottom 106 down so as to trap gas in a head space 110 within the closed top 104 of the cup 100 and trap a solution volume 112 of the aqueous solution near the open bottom end 106 of the cup 100. A vapor sensing transducer 114 is placed in the head space 110 for obtaining measurements of the volatile compound(s). The disadvantage of this approach rermiains the amount of time (days to weeks) for the gas in the head space 110 to reach equilibrium with the solution volume 112.
Accordingly, there is a need in the art of head space analysis of aqueous solutions for a method and apparatus reaching equilibrium in less than several days.
The present invention is an improvement to the method and apparatus for measuring volatile compounds in an aqueous solution. The apparatus is a chamber with sides and two ends, where the first end is closed. The chamber contains a solution volume of the aqueous solution and a gas that is trapped within the first end of the chamber above the solution volume. The gas defines a head space within the chamber above the solution volume. The chamber may be a cup with the second end open and facing down and submerged in the aqueous solution so that the gas defines the head space within the cup above the solution volume. The cup can also be entirely submerged in the aqueous solution. The second end of the chamber can also be closed such that the chamber can be used while unsubmerged, for example resting on a surface such as a bench. The improvement is a sparger for mixing the gas with the solution lo volume. The sparger can be a rotating element such as a propeller on a shaft or a cavitating impeller. The sparger can also be a pump and nozzle where the pump is a liquid pump and the nozzle is a liquid spray nozzle open to the head space for spraying the solution volume into the head space of gas. The pump could also be a gas pump and the nozzle a gas nozzle submerged in the solution is volume for spraying the head space gas into the solution volume.
An object of the present invention is to provide an apparatus and method for use in head space analysis of aqueous solutions which reduce the time needed to bring the head space gas to an equilibrium concentration of a compound within the aqueous solution.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.